Folding blade for a blown film line as well as blown film line with such a folding blade

ABSTRACT

The invention relates to a folding blade for a blown film line, as well as to a blown film line equipped therewith. 
     Folding blades are used for laterally folding in a film bubble running to the take-off pinch rolls. If they engage deeply into the film bubble, they are provided with a fin on the rear side, and referred to as deep folding blades. 
     The invention proposes that the rear side of a folding blade be equipped with a fin, which exhibits a collapsible element with an adjustment device. The volume of the fin can thereby be varied. In particular, the fin can be laid flat against the rear side of the folding blade.

The invention relates to a folding blade for a blown film line, as wellas to a blown film line with such a folding blade.

Blown film lines are used to a great extent to manufacture a variety offilm webs. In a blown film line, a plastic melt is first extrudedthrough a circular die using an extruder. The inside of the resultantmolten tube is pressurized with compressed air, so that the molten tubeexpands with increasing distance from the die. Reference is there madeto a tube formation zone. As the process continues, the melt-like filmbubble is cooled, and solidifies at the so-called frost line in modernsystems. It runs through a collapsing unit until reaching take-off pinchrolls. The take-off pinch rolls handle two functions: They pull up thefilm bubble at a preset rate on the one hand, and seal the film bubbleaway from the compressed air introduced into the interior on the other.

In some instances, it is desirable to feed the film bubble to thetake-off pinch rolls with folded-in sides. In particular, it isconceivable in this case that the film bubble be inflated to a pointwhere the resultant circumference would no longer have fit on thelay-flat width of the line when simply collapsed, i.e., the freelyusable width of the rolls in the take-off or a reversing unit oftensituated above the latter, or the other downstream equipment of theline.

Folding blades are known for folding in the sides of a film bubble. Inits simplest configuration, a folding blade consists of a mostly atleast triangular, elongated folding surface, with the wider base beingsituated below, i.e., upstream in relation to the direction ofextrusion. As the film gets pulled up by the take-off pinch rolls, thefolding surface becomes increasingly inclined toward the vertical axisof the film bubble, i.e., into the space that a simply ascending filmbubble would occupy. The excess pressure inside the film bubble pressesthe film surface against the folding surface. To the right and left ofthe folding surface, the excess pressure makes the film bubble try tooccupy the entire original space of the ascending film bubble. As aresult, folding flanks, i.e., sections of the film bubble extending tothe rear side of the folding surface, form on both sides of the foldingsurface of the folding blade.

The more the film ascends and the more narrowly the folding surface ofthe folding blade tapers, the larger the folding flanks of the filmbubble become.

If the folding blade projects into the ascending film bubble beyond acertain level perceived as critical, for example by more than 200 mm ormore than 250 mm, use is normally made of a so-called deep foldingblade. A deep folding blade initially consists of a folding blade withthe already described folding surface. On the rear side, i.e., on theside toward which the folding flanks extend, the upper end of thefolding blade is also provided with a fin, which protrudes toward theback from the folding surface. The fin ensures that the two foldingflanks now extending around the folding surface will only contact eachother to less of an extent, if at all.

DE 10 2007 029 794 B4 discloses a blown film line with two foldingblades, wherein the folding blades can be adjusted further into or outof the ascending film bubble.

Italian Laid-Open Patent Specification C 2007A000023 discloses a blownfilm line with a deep folding blade, wherein the deep folding bladeconsists of a triangular wedge with folding surface, and wherein therearward fin can be made to travel along the wedge, so that the wedgecan be outwardly displaced. A large, movable part of the fin is nowdownwardly displaced. An upper, fixed part of the fin is situated abovea part of the engine frame otherwise located in the path, and as aresult of the displacement, the downwardly moved part of the fin issituated below the part of the engine frame otherwise located in thepath.

For example, other folding blades and deep folding blades may be gleanedfrom DE 35 06 772 C2, Patent Specification DE 22 48 516, DE 25 10 515C3, U.S. Pat. No. 2,955,318, EP 0 457 304 B1, U.S. Pat. No. 2,961,930,U.S. Pat. No. 3,566,756, U.S. Pat. No. 3,897,530 or U.S. Pat. No.3,976,418.

The object of the present invention is to provide the known prior artwith a folding blade, a blown film line and a method.

In one aspect of the present invention, this object is achieved with afolding blade for a blown film line, with a folding surface for foldingin a film bubble running alongside, along with a fin protruding towardthe back from the folding surface for preventing folding flanksprojecting around the folding surface from coming into contact with eachother, wherein the folding blade is characterized in that the finexhibits a collapsible element with an adjustment device.

The following are terminological explanations:

The “folding surface” is meant to be the surface to be facing thevertical axis of the film bubble, along which the film bubble pulled bythe take-off pinch rolls can thus upwardly drift, and in so doing befolded in. In a simple case, the folding blade is formed, for example,by a plate made out of wood, metal and/or provided with plastic slidingparts and shaped like a triangle, with rounded edges and a thicknessnormally measuring several centimeters, and the folding surface issimply a surface of this plate.

The “rearward” alignment in principle is only obtained in a situationwhere the folding blade has been built into a blown film line. Ingeneral, however, the folding surface should be the side with which thefolding blade is to be aligned relative to the film web runningalongside, so that a rear side of the folding blade facing away from thevertical axis of the film bubble comes about on the opposing side. A finlocated there is to be viewed as rearward.

The “fin” can be configured in a variety of ways. The only requirementplaced upon it is that the folding flanks projecting around the foldingsurface be guided without damage upon contact. A more or less smoothsurface is therefore recommended, in particular one without any sharp,protruding elements.

The fin is usually only provided in an upper region of the foldingblade, for example in an upper half or upper third.

According to the aspect of the invention described above, the finexhibits a “collapsible element”. This must be understood to mean thatthe fin can reduce the size of its outer contours relative to eachother. An envelope around the fin in a non-collapsed state, i.e., in theexpanded state, thus has a larger volume than an envelope around thecollapsed fin.

Within the meaning of the invention present here, the collapsibleproperty only exists if the fin can be re-expanded. As known from U.S.Pat. No. 3,566,756, for example, a fin consists of wood. Therefore,while it can be reduced in terms of its volume through exposure to adestructively attacking force, it cannot be re-expanded. The inventiveidea present here is not intended to encompass destructive collapsing.

While the fin from the deep folding blade in C02007A000023 has a movableposition, it remains identical with respect to its volume, since boththe fixed upper part of the fin and the movable lower part of the finare each designed to be non-collapsible in terms of their volume.

The introduced aspect of the invention advantageously prevents anydisplacement by the fin or parts of the fin if so desired. Rather, thefin can simply be varied in terms of its size. As a result, it can notonly be adjusted to various fold-in depths, but, for example whensuitably configured, be laid flat so as to project toward the rear ofthe folding blade only very slightly or not at all. This gives thefolding blade a wide variety of uses, and allows it to be implementedwith simple and cost-effective technical means.

The “adjustment device” can in particular include any connecting meansfor applying force, air, another fluid or electrical current.

In a preferred embodiment, the collapsible element exhibits a bellows,and the adjustment device is designed as a volume adjustment device.

A “bellows” is to be understood as any component that exhibits atextile, soft, foldable and/or elastic sheath, in particular with astructural reinforcement situated therein or thereon. In particular, itmust be possible to expand a bellows by filling it with a fluid, andcollapse it by pumping or sucking out the fluid.

In a collapsible element designed in this way, the adjustment deviceacts as a volume adjustment device. This means that the adjustmentdevice is to be set up to expand or collapse the volume of the bellows,preferably in several stages or even continuously.

It can be provided that the bellows be outwardly sealed fluid tight,except for the connection to the adjustment device.

Another embodiment can provide that the bellows be semi-permeable indesign, wherein the adjustment device is connected and configured insuch a way that a stream of fluid can be supplied to the bellows so asto keep the volume of the collapsible element constant.

If an adjustment device exhibits a port for guiding fluid, thecollapsible element becomes especially easy to collapse and re-expand:All that need be done is to secure a line with a pump to the port. Ifthe pump then blows a fluid, air in the simplest case, into thecollapsible element, the collapsible element will expand. By contrast,if air is evacuated from the collapsible element, it will assume thecollapsed state.

Let it be noted that a pump does not necessarily have to be situatedoutside the collapsible element. Rather, enough installation space mightalso be available inside the collapsible element to set up practicallyindependent adjustment devices.

One example would be a hydraulic or pneumatic cylinder, which in thecollapsible element can ensure a resizing, for example hooked up to astabilizing framework inside the collapsible element, which then can besheathed with material or film, turning it into a bellows.

Independently force-applying elements can also be provided, for examplea return spring inside the collapsible element. In such a structuraldesign, it may be envisaged that the return spring brings thecollapsible element into a resting volume, with the volume of the finonly moving out of this state when an outer force is applied. When theforce is removed, the fin once again assumes the resting volume.

It is proposed that the fin exhibit a fixed element. In such a case, thefin is composed of at least two parts, specifically at least one fixedelement and at least one collapsible element.

Let it generally be noted that, within the framework of the presentapplication, indeterminate articles or numerical values are to beunderstood as minimum data. A term like “one . . . ”, “two . . . ”, etc.is thus always to be understood as “at least one . . . ”, “at least two. . . ”, etc., unless it may be gleaned from the respective context that“precisely one . . . ”, “precisely two . . . ”, etc. is meant.

As a rule, a fixed element will be more cost effective and technicallyeasier to construct than a collapsible element.

If a folding blade arranged on the blown film line exhibits regionswhere the rearwardly protruding fin does not hinder the variability ofuse, such a part can readily be fixed in place. The collapsible elementcan make sense in particular in a case where the folding blade mightotherwise collide with the engine frame when displaced or swiveled awayfrom the vertical axis of the film bubble, for example with a swingbearing, a bearing ring and/or a carrier ring, in particular of the kindthat is often encountered for an oscillation unit at roughly the heightof the take-off pinch rolls.

The fin can exhibit a guide for the collapsible element. The collapsibleelement can then be given a less stable design.

A guide for the collapsing element preferably is located on a fixedelement of the fin. For example, it can be a short rail or slidebearing, or a stably designed component of the collapsible element isguided inside the fixed element of the fin.

The collapsing element can exhibit a swiveling edge, wherein a loweredge is preferably designed like a hinge or otherwise pivoted. Aswiveling edge allows the edge to be swiveled on the folding bladeflatly or as flatly as possible around the pivot bearing on the lowerregion of the folding blade in the collapsing process. For purposes ofre-expansion, the swiveling edge can be pivoted back toward the rearwardside from the folding blade, once again around the hinge-like loweredge.

In a second aspect of the present invention, the set object is achievedby means of a blown film line with a folding blade as described above,wherein the folding blade is situated between a bubble expansion zoneand take-off pinch rolls, and the fin is aligned facing away from avertical axis for the running film bubble.

It is proposed that a connection be used to hook up the adjustmentdevice to an energy source of the blown film line, in particular to apump.

As has already been explained, the pump is set up in a preferredembodiment of the invention in such a way that it can pump in particularair or some other fluid into the collapsible element or pump it out ofthe collapsible element by way of a hose or pipe.

For example, another embodiment provides that the connection be a powercable, and the energy source of the blown film line be an electricalpower supply.

Alternatively or cumulatively, the connection can be a mechanicalconnection, for example comprised of gear wheels, knee levers or othermechanical structures.

In particular, the collapsible element is to be situated at the heightof a swing bearing or another frame part of the blown film line, whichwould otherwise collide with the fin as the folding blade or usual twofolding blades are swiveled or horizontally displaced on the line. It isprecisely there where it makes the most sense to provide a collapsibleelement.

The blown film line can ideally be moved into at least two or three orfour different folding operation modes by adjusting the collapsibleelement, specifically:

-   -   A deep folding operation mode, in which the folding surface and        fin are arranged so as to engage into the ascending film bubble,        and the fin protects the film bubble folded in from the folding        surface against its folding flanks coming into contact with each        other during operation, and/or    -   A first folding operation mode, in which the collapsible element        is present in the collapsed state, and the folding flanks of the        film web folded in from the folding surface still do not come        into contact with each other, and/or    -   A second folding operation mode, in which the collapsible        element is present in the collapsed state, and does not contact        the folding flanks of the film web folded in from the folding        surface, and/or    -   A non-folding operation mode, in which the folding surface of        the folding blade and the fin are varyingly positioned relative        to the folding operation types, so that they do not engage into        the ascending film bubble, wherein the fin is preferably        collapsed, so that the folding surface generates no folding        flanks during operation, and the blown film line flattens out        the film bubble without folding in.

In a third, independent aspect of the invention, the set object isachieved by a method for retrofitting or upgrading a blown film line,wherein a folding blade is installed as described above, if necessaryaccompanied by an expansion or modification of a folding blade or deepfolding blade or a lateral guide.

In a fourth aspect of this present invention, the set object is achievedby a method for operating a blown film line, in which a collapsibleelement of a fin is brought to a desired volume with an adjustmentdevice in order to set how deeply a folding blade or deep folding bladeengages into the ascending film bubble.

The invention will be described in greater detail below based on anexemplary embodiment, making reference to the drawing. Shown on:

FIG. 1 is a schematic, spatial view of a folding blade with acollapsible fin, and

FIG. 2 is a highly schematic, spatial view of an alternative foldingblade with a collapsible small fin.

From a structural standpoint, the folding blade 1 on the figureinitially consists of a triangular base plate 2. The base plate 2 ismade out of a wood-based material, and has rounded edges.

While facing the vertical axis of a film bubble, a front side 3 (coveredon the figure) is provided for purposes of immersion at an angle intothe film bubble pulled up by the take-off pinch rolls on a blown filmline.

The rear side of the folding blade 1 carries a fin 7. The fin 7essentially consists of a collapsible bellows 8 and fixed angle section9.

The bellows 8 is composed of a rigid plate 10 and soft cloth or film ona first flank 11 and on a second flank 12 (covered), wherein the flanks11, 12 join the rigid plate 10 with the base plate 2. The rigid plate 10is also joined with the base plate 2 inside the bellows by anarticulated mechanism 13 (not shown in detail).

In an upper region 14 of the bellows 8, the two flanks 11, 12 convergeand the rigid plate 10 tapers.

Two recesses 15 on the rigid plate 10 that otherwise runs with threestraight edges at a certain distance leave space for two edges 16, 17 ofthe angle section 9.

The rigid plate 10 is interrupted by an opening, to which a hose 19 isconnected by way of a fitting 18, so that the hose 19 can communicatewith the internal space of the bellows 8.

A pointed extension (covered by the leg of the angle section 9) of therigid plate 10 projects as far as into the angle section 9.

If air is pumped into the bellows 8 through the hose 19 duringoperation, the excess pressure inside the bellows 8 causes the rigidplate 10 to lift from the base plate 2 in a direction of expansion 20,specifically to pivot around the articulated mechanism 13. The movementcontinues until the two flanks 11, 12 are tensioned. The rigid plate 10then runs in alignment with the rearwardly averted edges of the anglesection 9.

By contrast, if air is sucked out of the bellows 8 through the hose 19,the bellows 8 collapses, and the rigid plate 10 comes to lie flat on thebase plate 2 along a collapsing direction 21 around the articulatedmechanism 13.

In both the collapsing and expanding process, the tip of the rigid plate10 is guided in the angle section 9.

A sealed hollow space can be provided inside the bellows 8 for the airthat was forced in and sucked out. The two flanks 11, 12 should thenform an essentially or hermetically tight seal with the rigid plate 10and base plate 2.

For example, it is simpler to provide a hydraulic cylinder between therigid plate 10 and base plate 2, which ensures the movement.

The labile flanks 11, 12 follow the movement of the rigid plate 10. Ifthe entire internal space of the bellows 8 is exposed to a vacuum in thecollapsing process, the two flanks 11, 12 are automatically retractedinto the interior during the collapsing movement, and hence do notendanger the film bubble. By contrast, if the internal space of thebellows 8 is not subjected to a vacuum in the collapsing process, it isadvisable that bands, e.g., rubber bands, be provided between the twoflanks 11, 12, so as to reliably fold the latter into the internalspace.

The alternative deep folding blade 22 on FIG. 2 has a fin 23 with atechnically very similar structural design. Therefore, no detaileddescription will be provided at this juncture.

From at technical standpoint, the fin 23 initially differs from the onefrom the embodiment described on FIG. 1 in that there is no fitting 18for compressed air. Provided instead is an electrical power line (notshown), which drives an adjustment system located inside the bellows.

However, a separate guide with a fixed part was omitted on an upper edge24 of the fin 23. As a consequence, the collapsible element embodied bythe fin 23 extends up until the upper edge 24 of the alternative deepfolding blade 22.

In terms of proportions, the fin 23 is only situated in an upper region25 of the alternative deep folding blade 22. For this reason, anarticulated mechanism 26 is not located on a lower side of the deepfolding blade, but rather further up, preferably above the center of thealternative deep folding blade 22. As a consequence, a base plate 27extends with a free part 28 under the fin 23 up to a lower edge 29 ofthe alternative deep folding blade 22.

REFERENCE LIST

-   1 Folding blade-   2 Base plate-   3 Front side-   4 Lower side-   5 Upper edge-   6 Rear side-   7 Fin-   8 Bellows-   9 Angle section-   10 Plate-   11 First flank-   12 Second flank-   13 Articulated mechanism-   14 Upper region-   15 Recesses-   16 Edge of angle section 9-   17 Edge of angle section 9-   18 Fitting-   19 Hose-   20 Direction of expansion-   21 Collapsing direction-   22 Alternative deep folding blade-   23 Fin-   24 Upper edge-   25 Upper region-   26 Articulated mechanism-   27 Base plate-   28 Free part-   29 Lower edge

1. A folding blade for a blown film line, with a folding surface forfolding in a film bubble running alongside, as well as with a finprotruding toward the back from the folding surface for preventingfolding flanks projecting around the folding surface from coming intocontact with each other, wherein the fin exhibits a collapsible elementwith an adjustment device.
 2. The folding blade according to claim 1,wherein the collapsing element exhibits a bellows and/or the adjustmentdevice is designed as a volume adjustment device.
 3. The folding bladeaccording to claim 1, wherein the adjustment device exhibits aconnection for a fluid guide.
 4. The folding blade according to claim 1,wherein the fin exhibits a fixed element.
 5. The folding blade accordingto claim 1, wherein the fin exhibits a guide for the collapsing element,preferably located on a fixed element of the fin.
 6. The folding bladeaccording to claim 1, wherein the collapsible element exhibits aswiveling edge.
 7. A blown film line with a folding blade according toclaim 1, wherein the folding blade is arranged between a bubbleexpansion zone and take-off pinch rolls, and the fin is aligned facingaway from a vertical axis of a film bubble.
 8. The blown film lineaccording to claim 7, wherein a connection is used to hook up theadjustment device to an energy source of the blown film line, inparticular to a pump.
 9. The blown film line according to claim 7,wherein the collapsible element is situated at the height of a swingbearing or another frame part of the blown film line.
 10. The blown filmline according to claim 7, wherein displacing the collapsible elementprovides two or three or four different folding operation modes tochoose from, specifically: a. A deep folding operation mode, in whichthe folding surface and fin are arranged so as to engage into theascending film bubble, and the fin protects the film bubble folded infrom the folding surface against its folding flanks coming into contactwith each other during operation, and/or b. A first folding operationmode, in which the collapsible element is present in the collapsedstate, and the folding flanks of the film web folded in from the foldingsurface still do not come into contact with each other, and/or c. Asecond folding operation mode, in which the collapsible element ispresent in the collapsed state, and does not contact the folding flanksof the film web folded in from the folding surface, and/or d. Anon-folding operation mode, in which the folding surface of the foldingblade and the fin are varyingly positioned relative to the foldingoperation types, so that they do not engage into the ascending filmbubble, wherein the fin is preferably collapsed, so that the foldingsurface generates no folding flanks during operation, and the blown filmline flattens out the film bubble without folding in.